36 



BOTANY AND PHARMACOGNOSY. 



They do not germinate at once, but on keeping them for six 

 months to a year they germinate readily on a culture medium 

 of potato, and retain their power of germination for years. 



Rust Fungi. — The Rust Fungi are parasitic on higher 

 plants and produce a thread-like, branching, cellular mycelium, 

 which develops in the tissues of the host. They differ especially 



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Fig. 23 . Spores of various Smuts, i , Ustilago longissima growing on the reed meadow- 

 grass {Panicularia americana) ; 2 , Ustilago Maydis from Indian com {Zea Mays) ; 3 , Ustilago 

 Oxalidis on the yellow wood-sorrel {Qxalis stricia); 4, Ustilago utriculosa on the Pennsyl- 

 vania persicaria (Polygonum pennsylvanicufn) . 



Germination of spores of Smuts. 5, Ustilago utriculosa, in water, showing promycelium 

 and sporidia; 6, Doassansia opaca from the broad-leaved arrow-head (Sagittaria laiifolia) 

 in water, showing promycelium, sporidia, and secondary sporidia which are falling 

 off; 7. Ustilago avenm from oat {Avena sativa) in horse dung, showing promycelium, and 

 lateral "infection threads" or hyphae; 8, germination of a sporidiuni of Ustilago Sorghi 

 into an infection thread; 9, small portion of a group of sporidia developed from promy- 

 celium of Tolyposporium eriocauli in potato agar; 10, cross section of epicotyl of broom- 

 corn infected by Ustilago Sorghi showing mycelium ramifying through parenchyma cells 

 of the cortex. — After Clinton. 



from the other Fungi in producing resting spores known as 

 TELEUTOSPORES. These spores consist of one or more cells sur- 

 rounded by a thick black wall, and they produce the " black rust " 

 seen on foliage at the end of the season. 



